The portably hydraulic jacks, which can usually be seen in the market, can be divided mainly into two different groups with respect to the positions of their hydraulic cylinders. The first kind, which will be referred to herein as a vertical jack in the following, has its hydraulic cylinder placed in a vertical position the lifting action is done directly by the protrusion of the piston rod. The second kind, which will be referred as a horizontal jack in the following, has its hydraulic cylinder placed in a horizontal position the lifting arm is raised by the cylinder through linkages. This invention relates mainly to the horizontal jacks.
For a horizontal jack, the linkages of the lifting arm can be pushed directly by the hydraulic cylinder, or else the linkages of the lifting arm can be pulled by a tension rod pivotally connected to the top of the piston rod of the hydraulic cylinder. With the addition of the tension rod, the overall length of the horizontal jack can be shortened and this will cut down the overall weight of the whole construction.
The conventional portable horizontal jack, especially the horizontal jack with tension rod, can only be operated by hand. However, it is desirable to have a compact horizontal jack which can be operated by hand or foot conveniently.